1. Field of the Invention
This invention relates to an image formation apparatus and in particular to an art for preventing condensation from occurring in an image formation apparatus and stably forming an image.
2. Description of the Related Art
Hitherto, an optical flat (photo scanner) for deflecting and reflecting a light beam emitted from a light source by a deflector such as a polygon mirror and scanning the light beam over the record face of a thermal development record material for recording an image has been installed in a thermal development record apparatus or an image formation apparatus such as a copier or a laser printer.
As this kind of optical flat, an apparatus using a semiconductor laser or a laser diode (LD) as a light source is known.
By the way, in a machine used in an environment in which air-conditioning facilities are not complete, for example, a medical image record apparatus (thermal development record apparatus), etc., installed in a vehicle, when it rains at high humidity or in a state in which the medical image record apparatus is cooled in the nighttime, if the ambient temperature rapidly rises because of starting up the machine, the dew-point temperature is reached and there is a possibility that condensation may occur in image formation apparatus. If condensation occurs in an optical system of a lens, a mirror, etc., forming a part of the image formation apparatus, a mark is left as a pattern in the optical system of the lens, the mirror, etc., still after the condensation is removed by drying water droplets, and the later formed image is adversely affected. Thus, once condensation occurs, the image formation apparatus must be cleaned; the image formation apparatus needs to be disassembled for cleaning in some cases.
Therefore, measures against condensation need to be taken at least for the optical system. Hitherto, image read machines have undergone dehumidification by a dehumidifier. However, installation of a dehumidifier causes an increase in the cost and the installation space of the dehumidifier is required, making it hard to compact the image formation apparatus; this is a problem. As other arts concerning condensation prevention, those for installing a thermal insulation heater or a fan are known (for example, JP-A-11-249534 (pages 3-5, FIG. 1), JP-A-5-107649 (pages 2-3, FIG. 1) and JP-A-9-292820 (pages 2-3, FIG. 1)).
An image formation apparatus disclosed in JP-A-11-249534 (pages 3-5, FIG. 1) includes a water droplet detection sensor, a thermal insulation heater, and a fan and when the water droplet detection sensor detects condensation, the fan is stopped to stop taking in outside air and the thermal insulation heater is turned on for heating and drying water droplets. However, in the image formation apparatus, after condensation occurs, the operation is started for drying water droplets or preventing furthermore progress of the condensation; initial occurrence of condensation cannot be prevented and the measures are not sufficient as the measures against condensation.
An image formation apparatus disclosed in JP-A-5-107649 (pages 2-3, FIG. 1) includes a thermal insulation heater in the proximity of a standby position of an optical system unit of a lens, etc., and after the optical system unit is moved to the standby position, the thermal insulation heater is turned on for heating and preventing condensation. Further, in an image formation apparatus disclosed in JP-A-9-292820 (pages 2-3, FIG. 1), when the image formation apparatus is started up, a fan is stopped to stop taking in outside air for a given time until the internal temperature rises, thereby preventing condensation. In the image formation apparatus disclosed in JP-A-5-107649 (pages 2-3, FIG. 1) or JP-A-9-292820 (pages 2-3, FIG. 1), particularly condensation in any other part than the standby position cannot be prevented and not only it takes a long time to start up the image formation apparatus, but also it is difficult to reliably avoid condensation.